This application is for further training of the candidate, Mitchell Knutson, who has a Ph.D. in Nutrition and post-doctoral experience in the molecular biology of iron metabolism. Dr. Knutson's immediate career goal is to acquire new skills and knowledge that will enable him to study iron metabolism in macrophages. To accomplish this task, Dr. Knutson will be mentored by Dr. Lester Kobzik, an expert in macrophage biology at the Harvard School of Public Health (HSPH), and co-mentored by Dr. Marianne Wessling-Resnick, his current mentor at HSPH. The research proposal will investigate the function of the newly identified protein, ferroportin, FPN1 (also known as MTP1 or IREG1), in iron metabolism in the macrophage. The hypothesis to be tested is that FPN1 plays a role in iron export from the macrophage after phagocytosis of red blood cells. Erythrophagocytosis by macrophages, with the subsequent release of iron into the circulation, constitutes the largest flux of iron within the body. The mechanism for this, however, is unknown. To investigate the role of FPN1 in the macrophage, immunofluorescence experiments will determine the subcellular localization of this protein. Cytolocalization will be assessed before and after erythrophagocytosis. FPN1 mRNA and protein expression will be measured after erythrophagocytosis, and the changes will be compared to changes in rates of iron release, as measured by the efflux of 59Fe after phagocytosis of 59Fe-labeled erythrocytes. To test the hypothesis that FPN1 plays a role in iron release, efflux of erythrocyte-derived 59Fe will be measured after overexpressing FPN1 in macrophages using retroviral vector transduction, as well as after suppressing FPN1 using antisense techniques. The proximity of experts in macrophage biology, retroviral transduction, and antisense technology at HSPH, combined with the local expertise of investigators in the iron field, offers Dr. Knutson a highly suitable environment for learning the necessary skills required to carry out the proposed experiments. Successful completion of these experiments will contribute significantly to our understanding of iron metabolism in the macrophage and will enable Dr. Knutson to advance towards his long-term career goal of becoming an independent investigator and Assistant Professor of Nutrition. Moreover, a better understanding of iron release from the macrophage is of considerable clinical importance given the disturbances in macrophage iron metabolism characteristic of hereditary hemochromatosis and the anemia of chronic disease.